(2) Example #2:A 0.5% (v/v) glacial acetic acid solution would contain 0.5

milliliters of glacial acetic acid in each 100 milliliters of solution.

d. When the type of percent is not stated, it is understood that dilutions of (1)

dry ingredient in a dry preparation are percent W/W, (2) dry ingredients in a liquid are

percent W/V, and (3) a liquid in a liquid is percent V/V.

a.

Ratio and proportion:

Formula:

IF # of parts = THEN

Amount of solute needed

100

Total volume or weight of product

b.

(1) Example #1:How many grams of zinc oxide are needed to make 240

grams of a 4% (w/w) zinc oxide ointment?

IF 4 g ZnO =

THEN

X g ZnO

100 g Oint

240 g Oint

is labeled as to what it represents. In the first ratio, the desired strength of the ointment

is indicated. A four percent zinc oxide ointment contains 4 grams of zinc oxide in each

100 grams of ointment and is labeled to indicate this. Because the question asks, "how

many grams of zinc oxide?," the X value must be placed opposite the grams of zinc

oxide in the first ratio (see above). The 240 grams of ointment is placed opposite the

grams of ointment in the first ratio.

Then: 100 X = 960

X = 9.6 g of zinc oxide

(2)

Example #2: How many milliliters of a 5% (w/v) boric acid solution can

be made from 20 grams of boric acid?

IF

THEN

5g

=

20 g

100 ml

X ml

5X

=

2000

X

=

400

MD0802

2-13

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